1. Field of the Invention
This invention relates to a system for supplying fluid under pressure and more particularly to a pressurised fluid supply system for a motor vehicle or the like which is provided with an internal combustion engine.
2. Description of the Prior Art
As is well know, there are three basic methods of supplying pressurised fluid in a motor vehicle. One is by connecting a pump to the crank shaft of the engine and using the power directly developed by the engine to drive the pump. Another is using the vacuum developed in the induction manifold to drive a vacuum motor which is in turn connected to a pump of some description, and the third is a pump driven by an electric motor which derives its power from the battery and/or the generator or alternator driven by the engine. The first is efficient in operation but is undesirable from the point of using valuable horsepower which would otherwise be transmitted to the driving wheels of the vehicle. This, when coupled with the already numerous devices which are driven directly by the engine, such as the generator or alternator, water pump, air conditioner (if fitted), oil pump (for engine lubrication) etc. lowers the effective output of the engine undesirably. The electrically driven pump being driven by or supplied with electrical power derived from an apparatus which like the mechanically driven pump, is driven by the crank shaft (i.e. generator or alternator) suffers from the aforementioned drawback of reducing the effective output of the engine (i.e. the power reaching the driving wheels of the vehicle). Another drawback suffered by this arrangement is that at night when a great percentage of the electrical equipment of the vehicle is employed (especially on rainy days) the total demand on the electrical system could prove too much causing the battery to be drained.